A hybrid-electric vehicle (HEV) may be configured to transfer torque from an engine and one or more electric machines to the traction wheels. The torque at the traction wheels is a function of the engine torque and the electric machine torques. A power-split architecture combines the driving torque generated by the engine and the torque generated by one or more electric machines in various operating modes.
A representative power-split architecture is illustrated in FIG. 1. The two electric machines, referred to as the motor and the generator, may be implemented by permanent-magnet AC motors with three-phase current input. The engine and the generator may be connected by a planetary gear set with the engine crankshaft connected through the mechanical damper to the carrier and the generator rotor connected to the sun gear. The mechanical damper functions to transfer torque from the engine to the driveline and compensates for short power spikes caused by operation of the engine. The damper acts as a filter and prevents short acting torque pulses from being transferred through the driveline. The mechanical damper may also delay a rapid change in engine torque from being transmitted to the drivetrain. A gear on the motor output shaft may be meshed to a counter shaft with a fixed ratio. The ring gear may also be connected to the counter shaft in a fixed ratio arrangement.
The driveshaft torque is a function of the motor torque and the ring gear torque. The ring gear torque is affected by the engine and generator torques. During a transient event in which engine torque is changing, the engine speed and ring gear speed may be different due to deflection of the mechanical damper. During these transient events, the engine torque may not immediately affect the driveshaft torque. It may be desirable use the faster acting motor to generate torque to fill in for the delayed engine torque. However, to provide a correct amount of additional torque to the motor, the amount of engine torque that is missing must be estimated. In the hybrid powertrain described, an estimate of the ring gear torque is an important quantity.
A prior art estimate of the ring gear torque is based on the generator torque and the generator inertia as follows:
            τ      ^        r    =            1      ρ        ⁢          (                        τ          g                -                              J            g                    ⁢                                    ω              .                        g                              )      where Jg is the lumped moment of inertia of the generator and the sun gear. This particular calculation of ring gear torque creates a positive feedback loop in some situations that may magnify driveline oscillations created by any disturbances. This calculation is also not robust to measurement noise and system disturbances. The calculation is based on the derivative of generator speed and noise on the generator speed signal may cause noisy derivatives that affect the accuracy of the estimation. The generator speed signal may be filtered but this may introduce unacceptable delays in the control system.